The present invention concerns data transfer over a network and pertains particularly to a media access controller capable of connecting to a serial physical layer device and a media independent interface physical layer device.
The IEEE 802.3 specification has been created and adopted as a method of sending information between computers and other devices. The IEEE 802.3u specification extended the technology for 100 megabits per second networking.
Within the IEEE 802.3 specification a physical sublayer (PHY) includes a Physical Coding Sublayer (PCS), a Physical Media Access (PMA) sublayer, and a Physical Media Dependent (PMD) sublayer. The PCS defines how data is encoded and decoded as well as how the Carrier Sense (CS) and Collision Detection (CD) functions work. The PCS also defines the interface between higher and lower layers in the protocol specification. The PMA defines the mapping of code bits, generation of a control signal (link_status), generation of control signals to the PCS, and clock recovery. The control signal (link_status) indicates the availability of the PMD. The control signals to the PCS indicate Carrier Sense, Collision Detection and Physical Layer Errors. The PMD defines the signaling method and parameters for the various physical parameters that are necessary to address the link's physical requirements.
The PHY is generally placed on a dedicated integrated circuit (chip). The PHY communicates with a separate media access control (MAC) integrated circuit. The MAC provides an interface to a host system. Some PHY chips provide connectivity for 10Base2 devices. For example, a PHY chip which provides connectivity to an attachment unit interface (AUI) (for 10Base2 connectivity) is available as part LXT908 from Level One Communications, Inc., having a business address of 9750 Goethe Road, Sacramento, Calif. 95827. PHYs which provide 10Base2 connectivity typically interface with a serial MAC chip.
With the advent of the IEEE 802.3u specification, some PHY chips provide connectivity to 10/100T networks. For example, a PHY chip which provides connectivity to 10/100 megabit networks is available as part LXT970 from Level One Communications, Inc. In order to connect a MAC chip to multiple PHY chips which can provide connectivity to 10/100 megabit networks or other types of media, a media independent interface (MII) bus was created. A PHY chip connected to an MII bus transmits to and receives data from a MAC chip in four bit groupings (nibbles) of data. For more information on construction of an MII bus, see Chapter 22 of the IEEE 802.3u specification.
Generally, to provide 10Base2 along with 10/100T connectivity, it is necessary to utilize two separate MACs. However Seeq Technology Inc. having a business address of 47200 Bayside Pky, Fremont, Calif. 94538-6567 has designed a specialized 10Base2 PHY which can communicate with a MAC over an MII bus. However, this solution requires the use of a specialized 10Base2 PHY.